The present invention relates generally to printers, and more particularly to a pinch roller actuating mechanism incorporated in such printers for moving pinch rollers toward and away from a platen to releasably lock a paper on the platen.
There are various known mechanisms for use in the printing unit of a printer for actuating pinch rollers to move toward and away from a platen for releasably locking a paper in position on the platen. A typical example of a known pinch roller actuating mechanism is shown in FIGS. 1 and 2 of the accompanying drawings. The printing unit in which the actuating mechanism is incorporated includes a cylindrical platen 1 rotatably supported on a side frame 7, a printing head 2 facing the front side of the platen 1, a paper chute 3 extending arcuately along a lower part of the platen 1 from the back to the front side thereof for defining, jointly with the platen 1, an arcuate paper feed passage, and a pinch roller 4 rotatably mounted on one end of the paper chute 3 adjacent to the printing head 2, the paper chute 3 being pivotably connected at its intermediate portion to a shaft 8 secured to the side frame 7. The pinch roller actuating mechanism includes a presser spring composed of a tension coil spring 5 acting on the other end of the paper chute 3 to pivot the latter about the shaft 8 in the clockwise direction to bring the pinch roller 4 into pressing engagement with the platen 1 (FIG. 1), and a horizontal release camshaft 6 rotatably supported at its opposite ends on the side frame 7 and engageable with the paper chute 3 to turn the latter counterclockwise about the shaft 8 against the bias of the pressure spring 5, thereby retracting the pinch roller 4 away from the platen 1 (FIG. 2).
To move the pinch roller 4 from the advanced paper-locking position shown in FIG. 1 to the retracted paper-releasing position shown in FIG. 2, the release camshaft 6 is turned about its own axis in the direction of the arrow A through an angle of about 90 degrees. With this angular movement, a cam follower 3a on the paper chute 3 is lifted by the camshaft 6, thereby causing the paper chute 3 to be turned in the direction of the arrow B against the bias of the pressure spring 5. As a consequence of the angular movement of the paper chute 3, the pinch roller 4 is retracted arcuately away from the platen 1 in a direction indicated by the arrow C.
The known printer incorporating such a pinch roller actuating mechanism has various drawbacks as follows: Since the release camshaft 6 and the paper chute 3 are structurally separated from one another and hence are required to be assembled with the side plate 7 separately, an automatized assembling of the printer is difficult to achieve. Another drawback is that the pressure spring 5 must have a spring force strong enough to urge the paper chute 3 and the pinch roller mounted thereon toward the platen 1. The release camshaft 6 is likely to be bent or deformed as it is always subjected to such a strong spring force. With the release camshaft 6 thus deformed, reliable paper supply is difficult to obtain.